In high pressure applications, metal-to-metal contact seals are preferred over elastomeric seals. To achieve adequate sealing, contact seals typically require that the contact stress exceed the pressure to be contained over a given sealing width. Contact seals used in high pressure tubular fittings, typically have initial make-up interference contact stresses at least an order of magnitude greater than the maximum pressure to be contained and distributed over very narrow widths to obtain adequate reliability. Calculations of the necessary contact stress are routinely performed using stress analysis methods such as finite element analysis.
Unfortunately, there are many applications in which it is desirable that the contact stress be minimized in order to facilitate assembly, sliding, rotation or other operations. In such applications, the high contact stress of metal-to-metal contact seals make them undesirable, as it inevitably leads to higher friction forces during relative movements and greatly increased potential for galling or other damage which can initiate seal failure.